Composites are combinations of two or more materials present as separate phases and combined to form desired structures so as to take advantage of certain desirable properties of each component. The materials can be organic, inorganic, or metallic, and in various forms, including but not limited to particles, rods, fibers, plates and foams. Thus, a composite, as defined herein, although made up of other materials, can be considered to be a new material have characteristic properties that are derived from its constituents, from its processing, and from its microstructure.
Composites are made up of the continuous matrix phase in which are embedded: (1) a three-dimensional distribution of randomly oriented reinforcing elements, e.g., a particulate-filled composite; (2) a two-dimensional distribution of randomly oriented elements, e.g., a chopped fiber mat; (3) an ordered two-dimensional structure of high symmetry in the plane of the structure, e.g., an impregnated cloth structure; or (4) a highly-aligned array of parallel fibers randomly distributed normal to the fiber directions, e.g., a filament-wound structure, or a prepreg sheet consisting of parallel rows of fibers impregnated with a matrix.
Monolithic ceramic materials are known to exhibit certain desirable properties, including high strength and high stiffness at elevated temperatures, resistance to chemical and environmental attack, and low density. However, monolithic ceramics have one property that limits their use in stressed environments, namely their low fracture toughness. While significant advances have been made to improve the fracture toughness of monolithic ceramics, mostly through the additions of whisker and particulate reinforcements or through careful control of the microstructural morphology, they still remain extremely damage intolerant. More specifically, they are susceptible to thermal shock and will fail catastrophically when placed in severe stress applications. Even a small processing flaw or crack that develops in a stressed ceramic cannot redistribute or shed its load on a local scale. Under high stress or even mild fatigue, the crack will propagate rapidly resulting in catastrophic failure of the part in which it resides. It is this inherently brittle characteristic which can be even more pronounced at elevated temperatures, that has not allowed monolithic ceramics to be utilized in any safety-critical designs.
Research and development for these high temperature and high stress applications have focused on the development of continuous fiber reinforced ceramic matrix composites, hereafter referred to as CFCCs. The use of fiber reinforcements in the processing of ceramic and metal matrix composites is known in the prior art, and has essentially provided the fracture toughness necessary for ceramic materials to be developed for high stress, high temperature applications. See J. J. Brennan and K. M. Prewo, “High Strength Silicon Carbide Fiber Reinforced Glass-Matrix Composites,” J. Mater. Sci., 15 463-68 (1980); J. J. Brennan and K. M. Prewo, “Silicon Carbide Fiber Reinforced Glass-Ceramic Matrix Composites Exhibiting High Strength Toughness,” J. Mater. Sci., 17 2371-83 (1982); P. Lamicq, G. A. Gernhart, M. M. Danchier, and J. G. Mace, “SiC/SiC Composite Ceramics,” Am. Ceram. Soc. Bull., 65 [2] 336-38 (1986); T. I. Mah, M. G. Mendiratta, A. P. Katz, and K. S. Mazdiyasni, “Recent Developments in Fiber-Reinforced High Temperature Ceramic Composites,” Am. Ceram. Soc. Bull., 66 [2] 304-08 (1987).; K. M. Prewo, “Fiber-Reinforced Ceramics: New Opportunities for Composite Materials,” Am. Ceram. Soc. Bull., 68 [2] 395-400 (1989); H. Kodama, H. Sakamoto, and T. Miyoshi, “Silicon Carbide Monofilament-Reinforced Silicon Nitride or Silicon Carbide Matrix Composites,” J Am. Ceram. Soc., 72 [4] 551-58 (1989); and J. R. Strife, J. J. Brennan, and K. M. Prewo, “Status of Continuous Fiber-Reinforced Ceramic Matrix Composite Processing Technology,” Ceram. Eng. Sci. Proc., 11 [7-8] 871-919 (1990).
Under high stress conditions, the fibers are strong enough to bridge the cracks which form in the ceramic matrix allowing the fibers to ultimately carry the load, and catastrophic failure can be avoided. This type of behavior has led to a resurgence of CFCCs as potential materials for gas turbine components, such as combustors, first-stage vanes, and exhaust flaps. See D. R. Dryell and C. W. Freeman, “Trends in Design in Turbines for Aero Engines,” pp. 38-45 in Materials Development in Turbo-Machinery Design; 2nd Parsons International Turbine Conference, Edited by D. M. R. Taplin, J. F. Knott, and M. H. Lewis, The Institute of Metals, Parsons Press, Trinity College, Dublin, Ireland, 1989. CFCCs have also been given serious consideration for heat exchangers, rocket nozzles, and the leading edges of next-generation aircraft and reentry vehicles. See M. A. Kamitz, D. F. Craig, and S. L. Richlin, “Continuous Fiber Ceramic Composite Program,” Am. Ceram. Soc. Bull., 70 [3] 430-35 (1991), and Flight Vehicle Materials, Structures and Dynamics—Assessment and Future Directions, Vol. 3, edited by S. R. Levine, American Society of Mechanical Engineers, New York, 1992. In addition, CFCCs with a high level of open porosity are currently being utilized as filters for hot-gas cleanup in electrical power generation systems, metal refining, chemical processing, and diesel exhaust applications. See L. R. White, T. L. Tompkins, K. C. Hsieh, and D. D. Johnson, “Ceramic Filters for Hot Gas Cleanup,” J. Eng. for Gas Turbines and Power, Vol. 115, 665-69 (1993).
CFCCs are currently fabricated by a number of techniques. The simplest and most common method for their fabricating has been the slurry infiltration technique whereby a fiber or fiber tow is passed through a slurry containing the matrix powder; the coated fiber is then filament wound to create a “prepreg”; the prepreg is removed, cut, oriented, and laminated into a component shape; and the part undergoes binder pyrolysis and a subsequent firing cycle to densify the matrix. See J. J. Brennan and K. M. Prewo, “High Strength Silicon Carbide Fibre Reinforced Glass-Matrix Composites,” J. Mater. Sci., 15 463-68 (1980); D. C. Phillips, “Fiber Reinforced Ceramics,” Chapter 7 in Fabrication of Composites, edited by A. Kelly and S. T. Mileiko, North-Holland Publishing Company, Amsterdam, The Netherlands, 1983; and K. M. Prewo and J. J. Brennan, “Silicon Carbide Yarn Reinforced Glass Matrix Composites,” J. Mater. Sci., 17 1201-06 (1982).
Other techniques for fabricating CFCCs also typically involve an infiltration process in order to incorporate matrix material within and around the fiber architecture, e.g. a fiber tow, a preformed fiber mat, a stack of a plurality of fiber mats, or other two dimensional (2D) or three dimensional (3D) preformed fiber architecture. These techniques include the infiltration of sol-gels. See J. J. Lannutti and D. E. Clark, “Long Fiber Reinforced Sol-Gel Derived Alumina Composites”, pp. 375-81 in Better Ceramics Through Chemistry, Material Research Society Symposium Proceedings, Vol. 32, North-Holland, New York, 1984; E. Fitzer and R. Gadow, “Fiber Reinforced Composites Via the Sol-Gel Route”, pp. 571-608 in Tailoring Multiphase and Composite Ceramics, Materials Science Research Symposium Proceedings, Vol. 20, edited by R. E. Tressler et al., Plenum Press, New York, 1986. Other techniques include polymeric precursors which are converted to the desired ceramic matrix material through a post-processing heat treatment. See J. Jamet, J. R. Spann, R. W. Rice, D. Lewis, and W. S. Coblenz, “Ceramic-Fiber Composite Processing via Polymer-Filler Matrices,” Ceram. Eng. Sci. Proc., 5 [7-8] 677-94 (1984); and K. Sato, T. Suzuki, Funayama, T. Isoda, “Preparation of Carbon Fiber Reinforced Composite by Impregnation with Perhydropolysilazane Followed by Pressureless Firing,” Ceram. Eng. Sci. Proc., 13 [9-10] 614-21 (1992).
Other research and development has involved molten metals that are later nitrided or oxidized. See M. S. Newkirk, A. W. Urquhart, H. R. Zwicker, and E. Breval, “Formation of Lanxide Ceramic Composite Materials,” J. Mater. Res., 1 81-89 (1986); and M. K. Aghajanian, M. A. Rocazella, J. T. Burke, and S. D. Keck, “The Fabrication of Metal Matrix Composites by a Pressureless Infiltration Technique,” J. Mater. Sci., 26 447-54 (1991). Other research and development has involved molten materials that are later carbided to form a ceramic matrix. See R. L. Mehan, W. B. Hillig, and C. R. Morelock, “Si/SiC Ceramic Composites: Properties and Applications,” Ceram. Eng. Sci. Proc., 1 405 (1980). Still other research and development has involved molten silicates that cool to form a glass or glass-ceramic matrix (see M. K. Brun, W. B. Hillig, and H. C. McGuigan, “High Temperature Mechanical Properties of a Continuous Fiber-Reinforced Composite Made by Melt Infiltration,” Ceram. Eng. Sci. Proc., 10 [7-8] 611-21 (1989)), and chemical vapors which decompose and condense to form the ceramic matrix (See A. J. Caputo and W. J. Lackey, “Fabrication of Fiber-Reinforced Ceramic Composites by Chemical Vapor Infiltration,” Ceram. Eng. Sci. Proc., 5 [7-8] 654-67 (1984); and A. J. Caputo, W. J. Lackey, and D. P. Stinton, “Development of a New, Faster, Process for the Fabrication of Ceramic Fiber-Reinforced Ceramic Composites by Chemical Vapor Infiltration,” Ceram. Eng. Sci. Proc., 6 [7-8] 694-706 (1985).
Two U.S. patents have issued which involve a method for the fabrication of a fiber reinforced composite by combining an inorganic reinforcing fiber with dispersions of powdered ceramic matrix in organic vehicles, such as thermoplastics. The first patent, U.S. Pat. No. 5,024,978, discloses a method for making an organic thermoplastic vehicle containing ceramic powder that can form the matrix of a fiber reinforced composite. This patent also discloses that the ceramic powder/thermoplastic mixtures can be heated to above the melt transition temperature of the thermoplastic and then applied as a heated melt to an inorganic fiber. This patent further discloses that the process may be used to make composite ceramic articles. The second patent, U.S. Pat. No. 5,250,243, discloses a method for applying a dispersion of ceramic powder in a wax-containing thermoplastic vehicle to an inorganic fiber reinforcement material to form a prepreg material such as a prepreg tow. This patent further discloses that the prepreg tow may be subjected to a binder pyrolysis step to partially remove the wax binder vehicle prior to consolidation of the prepreg tow into the preform of a composite ceramic article.
U.S. Pat. No. 5,936,861 discloses methods and apparatuses for making three-dimensional objects from continuous fiber reinforced composite materials. Slurry infiltration techniques are used to create a “prepreg” of reinforcement fiber and matrix material. The prepreg is formed into three-dimensional composite parts using a solid freeform fabrication process wherein the prepreg is extruded through a heated nozzle and deposited onto a base member and solidified.
To summarize, the continuous fiber reinforced ceramic composites (“CFCCs”) prior to the present invention have traditionally been fabricated using methods and apparatuses to infiltrate the matrix or matrix-forming material around a preformed architecture of dense fibers or fiber tows or by passing the fibers through a powder/melt slurry. While these methods and apparatuses provide a fiber reinforced composite structure, there is no control over the thickness of the matrix forming vehicle, and rarely will the matrix uniformly surround the fibers. In such methods, the fibers often contact each other which is detrimental to the mechanical behavior of such composites. In addition, these infiltration processes are quite slow, sometimes requiring weeks or months to fabricate components, and are severely limited in the matrix/fiber combinations that can be produced.
Furthermore, currently available techniques for fabricating continuous fiber reinforced composite objects are not suited for mechanically forming fully dense objects having complex geometries from continuous fiber-reinforced filaments from ceramic powder raw materials.
Thus, there exists a need for more efficient methods and apparatuses for applying the matrix to the fiber reinforcement. There exists a further need for methods and apparatuses that are versatile enough to allow almost limitless combinations of matrix and fiber reinforcement. There also exists a need for efficient methods and apparatuses for rapidly making three-dimensional objects, particularly objects having more complex geometries, from CFCCs, and particularly directly from computer aided designs (CAD).